Probably a query for any model engineers in da house

[Alf]

Actually, despite the subject line, this is probably for anyone who knows more about metal than I do - which is likely everyone.

So, I have this Pelikan mechanical pencil which is not working. The pen repair people are no use because they say "Buy a cheap one in bad condition for spare parts" and this is the cheap one in bad condition! Anyway, here it is exploded:



Not many pictures of their innards online, but usually they seem to be all brass, so I suspect this might be wartime manufacture - could be any time from 1937 to 1951 though. Whatever it is, it's very broken. If the brass collet is not held firmly in the end of the tube, the lead cannot be held at all, never mind extended.



Vital statistics are:
Tube: 3mm diameter, 2mm bore (as far as I can judge in that a 2mm HHS bit just went in)
Collet larger diameter: 2.5mm
Collet groove diameter: 2.1mm
Lead diameter: 1.18mm

Anyway, I would like to find a way to fix it. The existing tube is sufficiently mauled that I don't think it's long enough to work properly any more. I was thinking total replacement of the thin tube, which opens up a potential can of worms at the other end. Or possibly amputation and extension? The lead obviously needs to be able to get through, but I see there is such stuff as thin walled brass tube, and I wondered if some sort of inner sleeve could work and may be more doable with my (lack of) skill set. But then that's another place for joint failure.

But fundamentally, how is the collet held? I'm guessing it's a matter of heat, expansion of tube, insertion of collet, allow natural contraction do the job. In which case, what's the best heat source for such a task? In use this connection is held under pretty strong tension by that spring all the time, so it's got to be good. But equally I can't add any external bulk because the collet sleeve needs to slide over it all. Oh, and is it, as I assume, aluminium? And should I "upgrade" to brass, or will that make my life more difficult?

Ack, I have rambled, sorry. But a lot of ideas in my nut, and not the knowledge to know how best to progress. Any help most gratefully received.

Perplexed and pencil-less*, Al

*Not strictly true...

 

[novocaine]

the chuck and tube are rolled to form a lip that secures one inside the other. your one appears to have been separated at some time with a pair of pliers then a pair of grooves cut to let it close back up.

You have 2 options.
1. cut the tube and reroll the end, you will then need to shorten the barrel commensurately; or
2. replace the whole lead tube, which mean finding suitable material (look to old car arials ) it will be a friction fit (possibly shrunk) at the other end, but something like loktite 638 would help with the joint.

you can't make it any less broken at least.

 

[Woodster]

I think your chances of finding the correct size tube in a suitable material are pretty slim. You then have to fit it to the larger tube? If it were mine I’d try and find out the original manufacturer and go on a search for spare parts.

Edit: sorry, you did say Pelikan!

https://www.pelikanpens.co.uk/pages/spa ... ccessories

 

[novocaine]

the tube is a jellybean part, it won't have been drawn specifically for this application and I'd suggest a few measurements with the nearly rights (unless you have some decent measurement equipment) and a quick search maybe in order before we discount it.

connection at the other end is quite possibly a shrunk fit. stick the other part in the freezer overnight, quickly slip the tube on and let it heat back up. it's more likely the lead tube would have been heated, but without a bit of care it could all go wrong.

the harder part will be rolling the chuck end, the machine will have been made to measure with custom dies. with a strong wind I can make the dies But I'd want the pen here and I'm not really sure I have the time right now to offer to attempt to repair it.

material wise, I wouldn't have thought ali, I'd have thought steel,zinc, some random alloy.

 

[Alf]

Thank you, gentlemen.

Hmm, rolled at the chuck end had never occurred to me. I will investigate more about what that actually looks like and see if it fits the data I have before me. i.e. I will peer yet further at the mangled remains with a loupe. I do have a pic of one assembled, but am sworn to not share it (someone who is very conscious of IP rights and wotnot) and anyway the quality is not good, but it gave the impression of the tube being reduced down to the groove rather than built up, if that makes any sense. I was imagining it being crimped down with something like a pipe cutter, but with rollers rather than cutters.

Pelikan as a source are a dead end, as they have rather given up spares for 70 year old pencils; some companies have no idea of customer service at all... But a look about the interweb finds many examples of 3mm tube with an interior diameter of 2.1mm, which I wondered about. Funnily enough the defunct arial option had occurred to me just after posting.

Heigh ho, it's all a learning opportunity.

 

[Woodster]

These folks may be able to help with spares?

http://www.gutberlet.com/en/Produkte/Sc ... aniken.php

 

[Dalboy]

If none of the above work or not suitable for you then have you considered buy a new insert.

Try HERE

 

[novocaine]

I don't think I'm making sense Alf, sorry.
the end is reduced down, it is rolled over with a set of wheels not dissimilar to a pipe cutter, but with less of sharp edge.



you can see the lip that's formed into the grove on the chuck.

 

[MY63]

Try contacting Mark he had boxes of spare parts at the Newcastle pen show last month, I am sure he had some pencil parts in one of his boxes.
https://www.vintagepenparts.co.uk/oursh ... Parts.html

 

[Alf]

Dammit, Dave - how did you find such a good pic? My Google-fu is horribly weak these days. But yes, I think we're thinking the exact same thing, just that you know what you're talking about! I wonder if it would be feasible to adapt a mini pipe cutter... (Hallowe'en horror thought for you, I'm sure) Hmm, I shall have to see if I can dig out the one in the workshop and have a look at it. First need to dig out the workshop!

Woodster and Dalboy, nice thoughts, but lead size and wotnot is a problem. Modern mechanisms just aren't old-fashioned-friendly. Also I suspect that Gutberlet would be expecting orders in the 1000s, and then advise me to buy a Kaweco anyway ('cos they make them!)

Michael, yes, I aware of Mark, thank you.

Anyway, thank you, folks, for bending your minds to this. I am most grateful, and not quite yet daunted into giving up.

 

[novocaine]

would you mind taking some measurements for me Alf?
if you can get a caliper on the back end fitting to give me a lead tube inner diameter (ID) and measure the lead tube outer diameter (OD) I'll dig through the scraps and see what I can come up with.

you could possibly roll the end with on a drill press with a suitable form. I'll have a play when I can get past the mountain of kids bikes in the workshop (joys of nearly christmas).

 

[Alf]

I knew I'd rambled, 'cos they're in the first post but obviously easy to miss amongst the whitter. Here they are again.

Vital statistics are:
Tube: 3mm diameter, 2mm bore (as far as I can judge in that a 2mm HHS bit just went in - my Verniers aren't quite narrow-jawed enough to measure the back end)
Collet larger diameter: 2.5mm
Collet groove diameter: 2.1mm
Lead diameter: 1.18mm

But for heaven's sakes, please don't put yourself out. In better times my project planning to completion was generally measured in years. These days? Oi vey. :lol:

 

[novocaine]

my fault sorry. cheers, I'll take a look in the bits and bobs pile.